1894.] as a Chronometer of Geological Time. 147 



draining only the Erie basin. Then the Niagara river descended 

 200 ft. In course of time tbe waters subsided 220 ft. more, but 

 eventually they were raised again 80 ft. at the mouth of the Niagara, 

 thus reducing the descent of the river, from the head of the rapids 

 above the falls to the foot of the last rapids in its course to the lake, 

 to 320ft. During the lowest stage, Ontario lake receded twelve miles 

 from the end of Niagara gorge, where the falls had been located at 

 their nativity. 



9. Laws of Erosion. Theoretically the erosion varies as the height 

 of the falls and the volume of the water, but some of the work is 

 converted into heat. The recession is largely due to the work being 

 expended in the undermining of the hard capping rocks, by the 

 removal of the underlying shales. The rate of the modern recession 

 has been determined under the changing conditions of erosion, so 

 that the theoretical variations of other portions of the river's work 

 includes their modification. 



10 and 11. Episodes of the River and the amount of Recession in each. 

 Duration of each Episode. First episode : Water falling 200 ft., in 

 volume 3/11 of modern discharge ; gorge, 11,000 ft. long ; duration, 

 17,200 years. Second episode : river descending 420 ft., in three 

 cascades ; first stage, only the discharge of the Erie waters ; length of 

 chasm, 3,000 ft. ; duration, 6,000 years ; second stage, drainage of all 

 the upper lake ; length of chasm, 7,000 ft. ; duration, 4,000 years. 

 Third episode : same volume and descent as in last, but the three 

 falls united into one fall ; length of chasm, 4,000 feet ; duration, 

 800 years. Fourth episode : volume of water as at present, the level 

 of lower lake as to-day ; first stage, a local rapid making the descent 

 of 365 ft. ; work particularly hard ; length of gorge, 5,500 ft. ; dura- 

 tion about 1,500 years ; the second stage as at present ; work easy ; 

 length of canon, 6,000 feet ; descent of water, 320 ft. ; rate of reces- 

 sion here taken as the full measured amount of 4'175 ft. a year ; 

 duration, 1,500 years. Thus the age of the falls is computed to be 

 31,000 years, with another 1,000 years as the age of the river before 

 the nativity of the Falls. The turning of the Huron waters into the 

 Niagara was about 8,000 years ago, A difficult question was the 

 amount of work done in each episode. This was in part determined 

 by the position of the remaining terraces corresponding to different 

 stages of the river, and by the changing effects of erosion. 



12. Relations betiveen the Terrestrial or Epeirogenic Movements and 

 the Falls. The deserted beaches in the lake region have been deformed 

 by unequal terrestrial elevation, and this movement has caused the 

 changing conditions of the river in a large part, such as the turning 

 of the Huron waters from the Ottawa valley to the Erie basin. This 

 deformation affecting the Niagara district, since the commencement 

 of the river epoch, amounts to 2'5 ft. per mile ; east of Lake Huron, 



L 2 





